Microsoft word - hw chm 103 1-2010 stoichiometry.doc

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CHM 103 (1-2010) Problem Stoichiometry แสดงวิธีทํา
1. Which of the following equations are balanced? Balance any that need it.
(a) The thermite reaction, used in welding:
(b) The photosynthesis of glucose from CO2:
(c) The separation of gold from its ore:
Au + 2NaCN + O2 + H2O NaAu(CN)2 + 3NaOH
2. What are the molecular (formula) masses of the following substances?
(a) Hg2Cl2 (calomel, used at one time as a bowel purgative)
(b) C4H8O2 (butyric acid, responsible for the odor of rancid butter)
(c) CF2Cl2 (a chlorofluorocarbon that destroys the stratospheric ozone layer)
Answer (a) Hg2Cl2: 472.1 amu; (b) C4H8O2: 88.1 amu; (c) CF2Cl2: 120.9 amu
3. What is the molecular mass of cholesterol if 0.5731 mol weighs 221.6 g?
4. How many moles does each of the following samples contain?
(a) 1.0 g of chromium
(b) 1.0 g of gold
(c) 1.0 g of penicillin G potassium, C16H17N2O4SK

5. In the preparation of iron from hematite, Fe2O3 reacts with carbon:
Fe2O3 + C Fe + CO2 Unbalanced
(a) Balance the equation.
(b) How many moles of carbon are needed to react with 525 g of hematite?
(c) How many grams of carbon are needed to react with 525 g of hematite?
Answer (b) 4.93 mol; (c) 59.2 g C
6. Ethylene gas, C2H4, reacts with water at high temperature to yield ethyl
alcohol, C2H6O.
(a) How many grams of ethylene are needed to react with 0.133 mol of
H2O? How many grams of ethyl alcohol will result?
(b) How many grams of water are needed to react with 0.371 mol of
ethylene? How many grams of ethyl alcohol will result?
7. How many grams of solute would you use to prepare 167 mL of 0.200 M boric
acid (H3BO3) solution?
8. The sterile saline solution used to rinse contact lenses can be made by
dissolving 400 mg of NaCl in sterile water and diluting to 100 mL. What is
the molarity of the solution?
Answer 0.0685 M

9. Oxalic acid, H2C2O4, is a toxic substance found in spinach leaves. What is
the molarity of a solution made by dissolving 12.0 g of oxalic acid in
enough water to give 400.0 mL of solution? How many milliliters of 0.100 M
KOH would you need to titrate 25.0 mL of the oxalic acid solution
according to the following equation?

10. Calculate the mass percent composition of Prussian blue, an ink pigment:
Fe4[Fe(CN)6]3 .
11. What is the empirical formula of Ibuprofen, a headache remedy: 75.69% C,
15.51% O, 8.80% H ?
12. What is the empirical formula of Aspirin with the mass percent
compositions of Aspirin: 4.48% H, 60.00% C and 35.52% O ?
13. Combustion analysis of 45.62 mg of toluene, a commonly used solvent,
gives 35.67 mg of H2O and 152.5 mg of CO2. What is the empirical
formula of toluene?
Answer C7H8
14. Cytochrome c is an iron-containing enzyme found in the cells of all aerobic
organisms. If cytochrome c is 0.43% Fe by mass, what is its minimum
molecular mass?
Answer 13,000 amu
15. Give the percent composition of each of Saccharin, C7H5NO3S.
Answer 45.89% C, 2.751% H, 7.647% N, 26.20% O, 17.51% S
16. How many pounds of CO2 are produced from the complete combustion of
1.00 gal of gasoline. Assume that gasoline has the formula C8H18 and has
a density of 0.703 g/mL.
Answer 18.1 lb
17. A mixture of FeO and Fe2O3 with a mass of 10.0 g is converted to 7.43 g of
pure Fe metal. What are the amounts (in grams) of FeO and Fe2O3 in the
original sample?
Answer 4.4 g Fe2O3; 5.6 g FeO
18. A 1.268 g sample of a metal carbonate MCO3 was treated with 100.00 mL
of 0.1083 M H2SO4, yielding CO2 gas and an aqueous solution of the metal
sulfate. The solution was boiled to remove all the dissolved CO2 and was
then titrated with 0.1241 M NaOH. A 71.02 mL volume of NaOH was
required to neutralize the excess H2SO4.
(a) What is the identity of the metal M?
(b) How many liters of CO2 gas were produced if the density of CO2 is
1.799 g/L?
19. Window glass is typically made by mixing soda ash (Na2CO3), limestone
(CaCO3), and silica sand (SiO2) and then heating to 1500C to drive off
CO2 from the Na2CO3 and CaCO3. The resultant glass consists of about
12% Na2O by mass, 13% CaO by mass, and 75% SiO2 by mass. How
much of each reactant would you start with to prepare 0.35 kg of glass?


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